Dietary vitamin E supplementation inhibits thrombin-induced platelet aggregation, but not monocyte adhesiveness, in patients with hypercholesterolaemia

Several recent studies have indicated the possible beneficial effects of antioxidants, specifically vitamin E, in primary and secondary coronary prevention. These studies suggest that a diet enriched in vitamin E is insufficient to have a significant protective effect, whereas supplements, in excess of 200 international units (IU) per day, are efficacious in preventing coronary disease in both men and women. The mechanisms by which vitamin E may exert its protection are uncertain, but, vitamin E is lipophilic and has been shown to inhibit the oxidative modification of low density lipoprotein (LDL), a process thought to be of crucial importance in atherogenesis. We have also previously shown that α-tocopherol (the biologically most potent isomer of vitamin E) has important direct effects on vascular endothelial and smooth muscle cells. In the present study we have investigated the effects of oral supplements of vitamin E (400 IU per day) on platelet and mononuclear cell function in patients with hypercholesterolaemia. We found that although vitamin E supplementation had no significant effect on mononuclear cell adhesion ex vivo , it had a significant effect on the thrombin-induced platelet aggregation ( P  < 0.01; anova ): 6 weeks after starting the vitamin E supplements, the mean EC₅₀ for thrombin-induced aggregation increased 132% ( P  < 0.05; paired t -test) compared to treatment with placebo. The effects of vitamin E on platelet function may, in part, explain its anti-atherogenic properties.